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Structural Remodeling of Active Zones Is Associated with Synaptic Homeostasis

Huilin Hong, Kai Zhao, Shiyan Huang, Sheng Huang, Aiyu Yao, Yuqiang Jiang, Stephan Sigrist, Lu Zhao, and Yongqing Zhang


Journal of Neuroscience
DOI:10.1523/JNEUROSCI.2002-19.2020 


Abstract

Perturbations to postsynaptic glutamate receptors (GluRs) trigger retrograde signaling to precisely increase presynaptic neurotransmitter release, maintaining stable levels of synaptic strength, a process referred to as homeostatic regulation. However, the structural change of homeostatic regulation remains poorly defined. At wild-type Drosophila neuromuscular junction synapse, there is one Bruchpilot (Brp) ring detected by super resolution microscopy at active zones (AZs). In the present study, we report multiple Brp rings (i.e., multipleT-bars seen by electron microscopy) at AZs of both male and female larvae when GluRs are reduced. At GluRIIC-deficient neuromuscular junctions, quantal size was reduced but quantal content was increased, indicative of homeostatic presynaptic potentiation. Consistently, multiple Brp rings at AZs were observed in the two classic synaptic homeostasis models (i.e., GluRIIA mutant and pharmacological blockade of GluRIIA activity). Furthermore, postsynaptic overexpression of the cell adhesion protein Neuroligin 1 partially rescued multiple Brp rings phenotype. Our study thus supports that the formation of multiple Brp rings at AZs might be a structural basis for synaptic homeostasis.